The invention relates to a method for regenerating an activated-carbon canister that is laden with hydrocarbons. The activated-carbon canister is bound into a tank ventilation system of a fuel tank of an internal combustion engine and thereby adsorbs gaseous hydrocarbons that arise in the fuel tank. In the generic method, the activated-carbon canister is regenerated in a selected operating mode of the internal combustion engine, a flushing flow with hydrocarbons from the activated-carbon canister is conducted into an intake tract of the internal combustion engine downstream from a throttle element that is located in the intake tract, whereby flushing flow is fed to the combustion process, and whereby a deviation signal is evaluated, which is utilized as a measure of the hydrocarbon mass flow contained in the flushing flow. From that signal, it is possible to calculate a load level of the activated-carbon canister.
In addition to liquid fuel, there is always gaseous fuel present in the tank of a motor vehicle by virtue of the vapor pressure. Since the tank must have a ventilation opening to equalize pressure, hydrocarbons would continuously leak into the atmosphere due to the evaporation of fuel. That effect rises with the temperature of the fuel. Such hydrocarbon emissions can be prevented using activated-carbon canisters which are inserted into the ventilation line and which adsorb evaporated hydrocarbons from the tank. These measures are necessary in order to satisfy the regulatory limits with regard to evaporation losses.
The tank is thus ventilated only via an activated-carbon canister. Because the uptake volume of the activated carbon is limited, the activated-carbon canister, or rather the activated carbon therein, must be regenerated. To this end, while the internal combustion engine is running, environmental air is aspirated in via the activated-carbon canister, fed into the intake tract via a regeneration line, and delivered to the internal combustion engine for combustion. In this process the underpressure in the intake tract is exploited to suck in the air via the regeneration line. In order to keep the pollution emission within desirable limits without adversely affecting the run characteristics of the internal combustion engine, air that is sucked through the activated-carbon canister and is enriched with hydrocarbons therein must be purposefully conducted into the intake tract of the internal combustion engine, and the normal fuel metering must be corrected, for instance by an injection correction.
Commonly assigned U.S. Pat. No. 5,988,151, (German patent DE 107 01 353 C1), which discloses the generic method mentioned above, teaches that an injection correction such as this is accomplished by the lambda control that is already present in an internal combustion engine equipped with a three-way catalytic converter.
To this end, a control system controls a regenerating valve which is inserted in the regeneration line. By appropriately opening the regenerating valve, it is possible to set the flushing flow which is sucked in through the activated-carbon canister and led into the intake tract. The flushing mass flow is a function of the cross-section of the opening that is opened by the regenerating valve, the pressure difference between the intake tract and the atmosphere, and the temperature of the flushing flow.
But ultimately it is not the flushing flow that is critical, but the mass flow of the activated hydrocarbon that is introduced. This is a product of the flushing mass flow and the concentration of hydrocarbons in the flushing flow. This concentration is ultimately determined by the load level of the activated-carbon canister.
According to U.S. Pat. No. 5,988,151 (DE 197 01 353 C1), normal operation is guaranteed with the aid of a lambda control at lambda=1. Thus, it is possible to obtain a measure of the hydrocarbon mass flow that was introduced into the intake tract during regeneration from the unbalance of the lambda controller, along with a measure of the load level of the activated-carbon canister when the flushing flow is known.
Therefore, in internal combustion engines which are not driven with a lambda control or whose lambda signal is not indicated with sufficient resolutionxe2x80x94such as is the case with lean burn internal combustion engines in the stratified lean burn operationxe2x80x94this procedure is not possible.
The object of the invention is to provide a method for regenerating an activated carbon canister that is laden with hydrocarbons which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which allows the regeneration to occur independent of a lambda control.
With the above and other objects in view there is provided, in accordance with the invention, a method of regenerating an activated-carbon canister in a tank ventilation system of a fuel tank of an internal combustion engine adsorbing gaseous hydrocarbons from the fuel tank. The method comprises the following steps:
regenerating the activated-carbon canister in an idle operation of the internal combustion engine, during which the internal combustion engine is driven without lambda control;
conducting a flushing flow with hydrocarbons from the activated-carbon canister into an intake tract of the internal combustion engine downstream from a throttle element in the intake tract, and feeding the flushing flow to a combustion process;
reducing a fuel quantity to the internal combustion engine with an idle controller controlling the internal combustion engine by a differential to compensate for a hydrocarbon mass flow delivered with the flushing flow; and
evaluating the differential and calculating a load level of the activated-carbon canister.
In accordance with an added feature of the invention, a total mass flow of the flushing flow is determined as a function of an underpressure in an intake tract of the internal combustion engine and an opening angle of a regeneration valve switching the flushing flow into the intake tract, and computing the load level as a quotient of a hydrocarbon mass flow and the total mass flow of the flushing flow.
In accordance with an additional feature of the invention, a relationship between the reduced fuel quantity and the hydrocarbon mass flow is determined from an operating-parameter-dependent engine characteristic map.
In accordance with another feature of the invention, the flushing flow is increased continuously.
In accordance with a concomitant feature of the invention, the flushing flow is controlled by repeatedly opening and closing a regeneration valve connected to switch the flushing flow into the intake tract, and a duty factor of the repeated opening and closing is increased for constantly increasing the flushing flow.
In other words, the regeneration occurs when the internal combustion engine is idling, when it is driven without lambda control, for instance in a stratified lean burn operation. With the aid of a momentum-based idle controller, the no-load operation is held constant while the flushing flow rises in a sloping fashion. The idle controller responds to the hydrocarbon mass flow that is delivered with the flushing flow with a reduction of the fuel mass which is delivered, for instance by direct injection, to the internal combustion engine in the stratified lean burn operation. The resulting reduced fuel quantity is a measure of the hydrocarbon mass flow.
However, the delivered hydrocarbon mass flow does not lead exclusively to a speed-enhancing torque. A portion of the hydrocarbons that are delivered with the regeneration gives rise to a temperature elevation in the exhaust tract or manifests itself in elevated hydrocarbon emissions in the exhaust gas. This dividing of the effect of the hydrocarbons that are delivered with the flushing flow lends the method an additional robustness, since the reduced fuel quantity that must be taken into account by the idle controller is thus lower than the amount of hydrocarbons introduced with the flushing flow. Therefore, this situation is preferably expressed in an engine characteristic map that is obtained in advance, with the aid of which the reduced fuel quantity amount is correlated with the hydrocarbon mass flow. Once knowledge of the hydrocarbon mass flow is obtained in this way, the load level of the activated-carbon canister can be calculated, together with the total mass flow of the flushing flow, by forming the quotient of the hydrocarbon mass flow and the mass flow of the flushing flow. The latter is derivable as a function of the intake tube underpressure and the opening of the regeneration valve which is located between the activated-carbon canister and the intake tract and which is appropriately switched in order to set the flushing flow.
Once the load level of the activated-carbon canister is known, it is then possible to feed a hydrocarbon mass flow to the combustion process at arbitrary operating points of the internal combustion engine in a purposeful manner and to take this into account in the normal fuel metering (injecting) process accordingly.
Because of the higher stability of the idle controller due to the fact hat the hydrocarbons only partly give rise to a speed momentum, the inventive method has the advantage that in the stratified lean burn operation lower requirements are placed on the precision of the regeneration valve when the flushing flow must be increased in a sloping manner in known fashion. Finally, with the inventive method it is possible for the first time to determine the load level of the activated-carbon canister in operating phases in which a lambda control is not present and the lambda signal does not allow an inference to be made with sufficient exactness as to the hydrocarbon mass flow that is delivered with the flushing flow.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method for regenerating an activated-carbon canister, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.